I think I just had this problem myself.
I booked an award 2 days ago (domestic, AA metal) and this morning it was still in "Pending" status. IME, this never happens - they always ticket within a few minutes.
So I called in and they asked for a bunch of verification info about my account, and then said that they see an error with the transaction - that I couldn't use the card on file - needed an alternative form of payment (for the $5.60 tax). The "issue" with that card is that my card has only my first initial and last name on it. AmEx, FWIW.
Something has definitely changed recently. I've had this particular card on file w/ AA for many, many years.